As demand of a consumer has changed resulting from digitization and high performance of electronic products, a market demand is also changing to development of a power supply device with high capacity due to a thin profile, weight reduction, and high energy density.
To meet such demand of the consumer, a power supply device, which includes a lithium-ion secondary battery, a lithium-ion polymer battery, a supercapacitor (for example, an electric double layer capacitor and a pseudo capacitor), and the like which have high energy density and large capacity, is being developed.
In recent years, demand for mobile electronic devices including a portable telephone, a notebook computer, a digital camera, and the like is continuously increasing, and particularly, interest in a flexible mobile electronic device, to which a roll-type display, a flexible e-paper, a flexible liquid crystal display (LCD), a flexible organic light-emitting diode (OLED), and the like are applied, is increasing. Consequently, it is also needed for a power supply device for the flexible mobile electronic device to have a flexible characteristic.
As one of power supply devices capable of having such a flexible characteristic, a flexible battery is being developed.
The flexible battery may include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, a lithium-ion battery, and the like which have a flexible characteristic. Particularly, since the lithium-ion battery has high energy density per unit weight and is able to be rapidly charged compared to other batteries including a lead storage battery, a nickel-cadmium battery, a nickel-hydrogen battery, a nickel-zinc battery, and the like, it has high availability.
The lithium-ion battery employs a liquid electrolyte, and is mainly used in the form of a welded metal can as a vessel. However, since a cylindrical lithium-ion battery using a metal can as a vessel is fixed in form, there is a disadvantage in which an electrical product has limitation in design and further difficulty in reduction of a volume thereof.
Specifically, as described above, since the mobile electronic device is developed to be flexible as well as to have a thin profile and miniaturization, there is a problem in that a conventional lithium-ion battery using a metal can or a battery of a square-shaped structure is not easy to be applied to the mobile electronic device.
Therefore, to address the structural problem as described above, a pouch type battery, in which electrolyte is put into a pouch including two electrodes and a separator and then is sealed and used, is recently being developed.
There is an advantage in which such a pouch type battery may be manufactured with material having flexibility to be made in various forms, and may implement high energy density per weight.
That is, as shown in FIG. 1, a pouch type battery 1 is provided in a form in which an electrode assembly 20 is encapsulated inside an exterior material 10, and the exterior material 10 has a structure in which an inner resin layer, a metal layer, and an outer resin layer are stacked. The metal layer among these layers is an essential component of the exterior material for the purpose of a moisture proof and the like, and it serves to prevent moisture from penetrating from an outside of the exterior material into an inside thereof and at the same time to block electrolyte, which is located the inside of the exterior material, from leaking to the outside of the exterior material, since density of the metal layer is dense and thus the moisture and the electrolyte could not pass the metal layer.
Such a metal layer, however, has an insufficient elastic restoration force and thus it is difficult to secure flexibility over a predetermined level so that there is a problem in that a crack is caused when the metal layer is repeatedly bent.
Moreover, when the flexible battery is wound more than a single turn, distortion occurs at a portion exceeding the single turn and thus a crack of the flexible battery is caused so that there is limitation to manufacturing a flexible battery exceeding a predetermined length.